The subject invention relates generally to high solids image conditioning of liquid ink images, and in particular, to high solids image conditioning of liquid ink images by removal of liquid.
Generally, the process of electrophotographic copying is initiated by illuminating an original document with a light source to generate a light image of the original document. A substantially uniformly charged photoreceptive member is exposed with the light image to discharge the surface areas of the photoreceptive member that correspond to non-image areas in the original document while maintaining the charge in image areas. This selective discharging scheme produces an electrostatic latent image of the original document on the surface of the photoreceptive member. This latent image is subsequently developed into a visible image by a process in which developer material is deposited onto the surface of the photoreceptive member. Typically, this developer material comprises carrier granules having toner particles that electrostatically adhere to the charged areas of the latent image to form a powder toner image on the photoreceptive member.
Alternatively, liquid developer materials that include liquid carrier material in which toner particles are dispersed may be used. When liquid developer materials are used, the developer material is applied to the latent image with the toner particles being attracted toward the image areas to form a liquid image. Regardless of the type of developer material employed, the toner particles of the developed image are subsequently transferred from the photoreceptive member to a copy sheet, either directly or by way of an intermediate transfer member. Once on the copy sheet, the image may be permanently affixed to provide a xe2x80x9chard copyxe2x80x9d reproduction of the original document or file. The photoreceptive member is then cleaned to remove any charge and/or residual developer material from its surface in preparation for subsequent imaging cycles.
The above-described electrophotographic reproduction process is well known and is useful for light lens copying from an original, as well as for printing applications involving electronically generated or stored originals. Analogous processes also exist in other printing applications such as, for example, digital laser printing where a latent image is formed on the photoconductive surface via a modulated laser beam, or ionographic printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images. Some of these printing processes develop toner on the discharged area, known as DAD, or xe2x80x9cwrite blackxe2x80x9d systems, in contradistinction to the light lens generated image systems which develop toner on the charged areas, known as CAD, or xe2x80x9cwrite whitexe2x80x9d systems. The subject invention applies to both such systems.
When using liquid developer materials or toners, the liquid carrier medium needs to be removed from the photoconductive surface after the toner has been applied so the liquid carrier is not transferred from the photoreceptor to the paper or to the intermediate medium and then to the paper during image transfer. Removing the liquid carrier also allows it to be recovered for recycling and reuse in the developer system. This provides additional cost savings in terms of printing supplies and helps eliminate environmental and health concerns that result from the disposal of excess liquid carrier medium.
One known method of removing excess carrier fluid from a developed image requires placing a blotter roll in rotatable contact with the image while it resides on the photoreceptor or intermediate substrate. The blotter roll is typically made from an absorbent material, which allows the excess carrier fluid to be drawn from the surface of the photoreceptor or intermediate substrate and into the contacting roll. The fluid is then removed from the roll via a vacuum applied to the interior cavity of the roll. Removal of carrier fluid from the surface of the image results in an increase in solid particle content, increasing the efficiency of the transfer of the image from the photoreceptor to the intermediate substrate or from the intermediate substrate to permanent media. However, vacuum alone has a limited ability to remove the carrier liquid from the blotter roll.
The solid content of the toner particles can be increased to 40% or higher if a High Solids Image Conditioning (HSIC) unit is used. One form of a HSIC unit includes a high contact pressure blotter roll or squeegee roll that presses against the photoreceptor or intermediate transfer belt (ITB) and squeezes the liquid carrier out of the photoreceptor or ITB via mechanical compaction. A problem is that there is a limit to how much liquid carrier may be squeezed out of the photoreceptor or ITB by applying high pressure to increase the solid particle content. Squeegee roll methods have difficulty in removing the liquid from the interstices of a highly packed particle layer primarily because air does not flow in the narrow liquid- and solid-filled nip between the blotter roll and the compacting roll that pushes the image carrier into engagement with the blotter roll.
FIG. 1 is a plot of the solids content percentage of a developed image versus nip pressure in a known squeegee roll image conditioning method. As indicated by the trend of the data in FIG. 1, a solids content fraction above approximately 50% cannot be attained. Pressures as high as 100-200 psi in the nip may be required to increase the toner solids content to 40% solid particles by weight in the image. Such high nip pressure creates a drag on the photoreceptor belt or ITB and motion quality control issues.
Another known form of a HSIC unit for removing excess carrier fluid from a developed image evaporates the carrier liquid directly from the image. Such an evaporating HSIC requires heat management on the substrate and/or the ITB, a high volume of air flow, and high power consumption. In transfuse systems, heat management is difficult to implement on the thick conformable members required for good media latitude. Another problem is that liquid carriers that may be evaporated may present environmental issues.
The most efficient conditioning of an image to increase the percentage of solids content obviously requires preventing the solid toner particles from leaving the image while removing the carrier liquid. Successful image conditioning also requires electrostatic forces to hold or stabilize the toner particles in order to increase the clarity and resolution of the toner image. In addition, the carrier liquid removal device must also remain clean and free of toner particles so as to prevent it from thereafter contaminating a subsequent image with embedded toner particles.
Various techniques and devices have been devised for conditioning the liquid developer image by using blotter rolls or rollers to remove carrier liquid from the image as discussed above. Using one method, the developed image containing approximately 8% to 10% solid particles is first subjected to treatment by a Low Solids Image Conditioner (LSIC) which increases the percentage of solids to approximately 14% to 20%, while increasing the stability of the image, and reducing the thickness of the background fluid. High Solids Image Conditioning (HSIC) is then applied in order to increase the solid particle content to approximately 40%-45%, enabling the image to be transferred and fixed to a fmal substrate, without removing solid particles along with the carrier fluid.
The application of high contact pressure to the image, as described earlier, unfortunately results in the offset of a substantial amount of the toner particles to the blotter surface when the input image reaches higher toner concentrations. Thus, it is advantageous to devise a way in which the solid particle content of an image developed using a liquid material may be substantially increased without requiring a high contact pressure to be applied to the surface of the image. The application of high contact pressure may also result in a mechanical drag on the movement of the photoreceptor.
Accordingly, there is a need for a method of High Solids Image Conditioning (HSIC) that does not rely on the application of high contact pressure to the image-bearing member (IBM) to remove liquid carrier from the image. There is also a need for a method of High Solids Image Conditioning (HSIC) that achieves a higher toner solids content percentage without mechanically dragging the IBM movement. Further, there is a need for a method of High Solids Image Conditioning (HSIC) that does not require carrier fluid evaporation, high power consumption or the use of liquid carriers that present environmental issues.
The above needs, as well as others, are fulfilled by providing a system having an air knife to directly or indirectly remove liquid carrier from an IBM. The air knife may be applied directly to the IBM to blow carrier liquid out of the IBM into a container or blotting roll. Alternatively, a blotting belt may be pressed against the IBM in order to absorb carrier liquid and an air knife may be used to blow carrier liquid out of the blotting belt to restore its absorption properties. Thus, the air knife improves the effectiveness of the blotting belt in removing liquid carrier from the image transporter without requiring nip pressures that distort the image.
In embodiments of the invention, an arrangement includes at least one movable image bearing member transporting a latent image in an electrophotographic printing system. A developer station associated with the at least one image bearing member deposits a developed image on the latent image. The developed image includes toner particles and carrier liquid. A transfer station associated with the at least one image bearing member transfers the developed image to a receiving medium. A liquid removal station disposed between the developer station and the transfer station includes a source of high fluid pressure emitting a jet of fluid that removes at least a portion of the carrier liquid from the developed image. The fluid jet may remove the carrier liquid directly from the image bearing member or it may indirectly remove carrier liquid from the image bearing member by blowing carrier liquid from a blotting belt or the like.
The method of the present invention includes transporting a latent image containing liquid carrier and toner particles on a porous substrate and directing a jet of fluid against the latent image to blow liquid carrier from the porous substrate. The method may also include providing a vacuum proximate to a surface of the porous substrate to remove liquid carrier blown from the substrate. In an alternative method of the present invention, the method includes applying fluid pressure against a portion of a blotting belt to remove liquid carrier from the blotting belt and contacting a latent image being carried by a porous substrate with the portion of the blotting belt from which the fluid pressure removed liquid carrier. This alternative method may further include cleaning the blotting belt with fluid to remove toner particles from the blotting belt.
The systems and methods of the present invention provide high toner solids content percentage without requiring heat for carrier liquid evaporation or the application of high pressure to the IBM to squeeze carrier liquid out of the belt. Thus, the removal of carrier liquid from the image can be performed more efficiently with less effect upon the image quality.
The above discussed features and advantages, as well as others, may be readily ascertained by those of ordinary skill in the art by reference to the following detailed description and accompanying drawings.